Mechanical drive units for operating doors and gates exist in the prior art. Such units typically employ limit switches to sense when the door or gate reaches either its fully open or fully closed position, after which they shut off. Such switches add to the complexity, cost, and maintenance of door operating devices. My previous U.S. Pat. No. 4,821,456, hereby incorporated into this application by reference, teaches a linear mechanical drive unit that does not require such limit switches.
While many existing drive units are suitable for low-shock environments, such as found in a typical residential garage, many door operating devices exist in harsh environments that often undergo severe shock and vibration. For example, automated door operators for cargo truck doors frequently experience rough road conditions, harsh loading procedures, and the like. A typical garage door opener adapted to operate a cargo truck door quickly becomes damaged and inoperative. As a result, conventional door operating units are not well-suited for harsh environments.
Clearly, then, there is a need for a rugged, shock-resistant automated door operator that does not require limit switches or other sensitive adjustment mechanisms. Such a needed device would be able to withstand considerable shock and vibration without being damaged, and would expose no mechanisms that are vulnerable to damage by such shock forces. Such a needed device would provide hysteresis between movement of the door and movement of the prime mover of the device in order to provide shock isolation between the door and the prime mover. Further, such a needed device would rigidly lock the door in the closed position, preventing manual opening of the door. However, such a needed device would provide a safety release means for manually opening the door in the event of a power failure, or the like. The present invention fulfills these needs and provides further related advantages.